(Coilostele acus)

This species was described in 1854, the type material, however, was apparently lost during World War II, thus the taxonomic validity of this taxon is unclear.:

“Taxonomic issues arose concerning two species when they were submitted to experts, although they had never been reported as nonvalid species in the scientific literature; because their taxonomic status is unclear (the biological species designated by their names are unknown), they were classified as impossible to assess. However, due to this taxonomic uncertainty, no data are available apart from their original 19th-century descriptions, and the model evaluates them as extinct. These taxa are Coilostele acus and Perrottetia piriformis.” [1]

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It is quite unlikely that this taxon is indeed extinct, it is most likely synonymous with some of the other species described in that genus. [2]

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References:

[1] Claire Régnier; Guillaume Achaz; Amaury Lambert; Robert H. Cowie; Philippe Bouchet; Benoît Fontaine: Mass extinction in poorly known taxa. Proceedings of the National Academy of Sciences. 1-6. 2015
[2] A. Martínez-Ortí; M. Prieto; F. Uribe: Addendum to the type catalogue of the malacological collection in the Museu de Ciències Naturals de Barcelona. Arxius de Miscel.lània Zoològica 16.2018

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edited: 09.11.2021